When electric currents are switched off in electromechanical switching devices, a switching arc occurs when the contacts are opened. The arc heats up the air in the switching chamber, which leads to an increase in pressure and consequently to an emission of the heated gases through discharge openings—hereinafter referred to as discharge. These heated and conductive gases also contain solid particles in dispersed form, and depending on their composition and gas temperature are conductive to different extents, even after leaving the installation equipment. The processes during discharge (temperature and chamber pressure) must be taken into consideration in the design of switching chambers (rigidity of the housing).
A large part of the arc energy is already absorbed inside the switching chamber by the chamber walls. In order to cool and split the switching arc, extinction plates which bring about the rapid extinction of the arc are normally used in circuit breakers. This arc cooling process inside the switching chamber occurs at a high temperature level and takes place primarily through radiative transfer.
The hot discharged gases are electrically conductive and can generate arcs outside of the installation equipment between live parts and cause damage unless sufficient clearance from adjacent, conductive and potentially live parts is maintained.
A cooling device in low-voltage circuit breakers is known, where a fine mesh metallic grille or grate is used (EP 0817223 B1).
Other inventions are also concerned with the cooling of the discharge; for example in U.S. Pat. No. 7,488,915 B2 or in DE 102010034264 B3. In these solutions, however, the flow is deflected multiple times. Disadvantages of these arrangements are that a build-up of pressure resulting from the flow deflection occurs along the cooling device and has an adverse effect on the switching characteristics. If one wishes to avoid this effect, an enlargement of the cross section must be undertaken. As a result of the complex flow control (including many deflections) and the delicate structure, blockages of the flow passages caused by particles in the discharge and damage to the mesh can occur in the case of fine gauge cooling meshes (EP 0817223 A1).
DE 1640265 A1 describes a cascade of cooling devices, where plates at the exit of a precooler are angled, the intention being to make it more difficult for arcs to return. Furthermore, DE 35 41 514 A1 describes an arc extinguishing chamber with an attachment for further cooling of the escaping gases.